1. Field of the Invention
This invention relates to an electrophotographic apparatus, a process cartridge and an electrophotographic photosensitive member. More particularly, it relates to an electrophotographic apparatus having a specific image-forming means and an electrophotographic photosensitive member with specific physical properties, and a process cartridge and an electrophotographic photosensitive member which are used for such an electrophotographic apparatus.
2. Related Background Art
As electrophotographic photosensitive members used in copying machines, laser printers and so forth, there are many electrophotographic photosensitive members which utilize organic photoconductors because of the advantages that they have a high safety, are suited for mass production, and may require a low cost. In particular, multi-layer type electrophotographic photosensitive members having a charge generation layer and a charge transport layer enable improvement in sensitivity, and hence they prevail among organic electrophotographic photosensitive members available in recent years.
Meanwhile, in order to obtain images with a higher image quality, or in order to store inputted images or edit them at will, the formation of images is rapidly being digitized. When images are digitally formed, digital electrical signals are converted into light signals, which are then inputted to an electrophotographic photosensitive member. As light sources used therefor, lasers and LEDs (light-emitting diode) are chiefly used. At present, the light sources most widely used emit light with an oscillation wavelength of 790xc2x120 nm. Accordingly, research has been conducted on electrophotographic photosensitive member materials having sufficient sensitivity in this wavelength region.
In particular, phthalocyanine compounds are widely studied and have been put into practical use as charge-generating materials, because many of them can be synthesized relatively easily and exhibit sensitivity in a long-wavelength region. Those showing especially high sensitivity include oxytitanium phthalocyanine, and those showing a variety of crystal forms have been studied as disclosed, e.g., in Japanese Patent Applications Laid-open No. 61-239248, No. 62-67094, No. 1-17066, No. 3-54264 and No. 3-128973.
However, in instances in which images are formed using the electrophotographic photosensitive member having a charge generation layer containing such a phthalocyanine compound as a charge-generating material and a charge transport layer, carriers generated in the charge generation layer upon exposure to light tend to remain therein because the phthalocyanine compound has high sensitivity, bringing about a disadvantage that any carriers having remained tend to cause variations of potential when images are formed on the next rotation of the electrophotographic photosensitive member. In particular, in the case of an electrophotographic apparatus not having any means for initialization (charge elimination or erasure), such as pre-exposure or the like, performed on the electrophotographic photosensitive member after a series of image formation steps, i.e., charging, exposure, development and transfer, have been completed and before it is charged for the next image formation operation (hereinafter also xe2x80x9ceraseless electrophotographic apparatusxe2x80x9d), what is called a xe2x80x9cghostxe2x80x9d, which is a phenomenon that an image formed on a previous one round of image formation of the electrophotographic photosensitive member comes to appear on the next image, has tended to occur when halftone images are reproduced.
An object of the present invention is to provide an electrophotographic apparatus which can enjoy high sensitivity, may cause no ghost at the initial stage and also when used repeatedly, and has superior image stability.
Another object of the present invention is to provide a process cartridge and an electrophotographic photosensitive member which are used for such an electrophotographic apparatus.
More specifically, the present invention is an electrophotographic apparatus comprising an electrophotographic photosensitive member around which a charging means, an exposure means, a developing means and a transfer means are provided in this order;
the electrophotographic apparatus not having any charge elimination means between the transfer means and the charging means; and
the electrophotographic photosensitive member being an electrophotographic photosensitive member comprising a support and provided thereon a charge generation layer containing a phthalocyanine compound and a charge transport layer, and the electrophotographic photosensitive member having a light-area dark attenuation rate A and a dark-area dark attenuation rate B which satisfy the following expression (1):
1.0xe2x89xa6light-area dark attenuation rate A/dark-area dark attenuation rate Bxe2x89xa61.7xe2x80x83xe2x80x83(1);
A=(|surface potential immediately after second-round charging of electrophotographic photosensitive member regarding first-round surface potential as light-area potential|xe2x88x92|surface potential after leaving for one second in dark immediately after second-round charging of electrophotographic photosensitive member regarding first-round surface potential as light-area potential|)/|surface potential immediately after second-round charging of electrophotographic photosensitive member regarding first-round surface potential as light-area potential|; and
B=(|surface potential immediately after second-round charging of electrophotographic photosensitive member regarding first-round surface potential as dark-area potential|xe2x88x92|surface potential after leaving for one second in dark immediately after second-round charging of electrophotographic photosensitive member regarding first-round surface potential as dark-area potential|)/|surface potential immediately after second-round charging of electrophotographic photosensitive member regarding first-round surface potential as dark-area potential|.
The present invention also provides a process cartridge and an electrophotographic photosensitive member which are used for the electrophotographic apparatus described above.